1. Field of the Invention
This invention relates to a rotating head type reproducing apparatus, and more particularly, to a reproducing apparatus arranged to reproduce an information signal by means of rotating heads and to detect a tracking error by using signals reproduced from the rotating heads.
2. Description of the Prior Art
The conventional apparatuses of the above-stated kind include video tape recorders (hereinafter referred to as VTR's) of the type performing tracking control in a manner called the four-frequency method. The present specification takes up, by way of example, the VTR of this type in describing this invention.
FIG. 1 of the accompanying drawings shows a pattern in which recording is made by the VTR of the above-stated type on a magnetic tape. This illustration includes a magnetic tape 1; and a group of recording tracks. Reference symbols f1, f2, f3 and f4, respectively, represent the frequencies of pilot signals superimposed on the video signal recorded in these recording tracks. These different frequencies are arranged to be, for example, as follows: f1=102.5 KHz.apprxeq.6.5 fH, f2=118.9 KHz.apprxeq.7.5 fH, f3=148.7 KHz.apprxeq.9.5 fH, and f4=165.2 KHz.apprxeq.10.5 fH, wherein fH represents a horizontal scanning frequency. Generally, these frequencies are arranged to be in the following relation: f4-f3=f2-f1 and f2.noteq.f3.
Rotating heads Ha and Hb have different azimuth angles. The head Ha is arranged to perform a recording or reproducing operation in or from the tracks TR1 and TR4 in which the pilot signals of frequencies f1 and f4 are superimposed on the video signal. The other head Hb is arranged to record or reproduce in or from the tracks TR2 and TR3 in which the pilot signals of frequencies f2 and f3 are superimposed on the video signal. The spacing distance between one track and another is arranged to be shorter than the width of these heads Ha and Hb. During recording, a recording operation called azimuth overlapped writing is accomplished in a known guard-band-less manner.
In the VTR of this kind, a tracking error signal is arranged to be obtained in the following manner: When the reproducing rotary head is in an on-track state as in the case represented by FIG. 1, the head reproduces the video signal while the pilot signals superimposed on the adjacent tracks on both sides of the track which is mainly traced under control (hereinafter referred to as the main track) are also reproduced by the same reproducing head. This is because, compared with the frequency of the video signal, each pilot signal is sufficiently low to bring about no azimuth loss. Therefore, by comparing the levels of the pilot signals reproduced from the adjacent tracks on both sides of the main track with each other, the position of the head relative to the main track can be detected. A tracking error signal is thus obtained on the basis of the result of the level comparison.
In the case of the arrangement made to obtain a tracking error signal by the above-stated four-frequency method, an accurate tracking error signal is obtainable if the width of a reproducing head is the same as that of a recording head and the record is recorded without any guard band.
FIG. 2 shows a recording pattern on a magnetic tape having a guard band formed between one recording track and another. The frequencies f1, f2, f3 and f4 are arranged in the same manner as in the case of FIG. 1. If a tracking error signal is obtained by the above-stated method while a head Ha is tracing a recording track TR1, the tracking error signal would remain unchanged irrespectively of the position of the head as long as it is between the positions Ha' and Ha". It is, therefore, impossible to accurately perform tracking control. In this instance, therefore, the magnetic tape 1 is generally traced with the head Ha allowed to change its position between the positions Ha' and Ha" depending on the characteristic of the servo system of a capstan which is arranged to cause the tape to travel. It is, therefore, hardly possible to satisfactorily reproduce a video signal from a recording pattern in which the guard bands are formed.
Meanwhile, some of the known VTR's have been arranged to be capable of recording over a long period of time by forming recording tracks at a narrower track pitch than the ordinary recording tracks. However, if recording and reproduction are to be carried out at such a different track pitch by the VTR of the kind performing the four-frequency type tracking control, it becomes necessary to arrange the recording or reproducing head to have a wider head width than the track pitch employed for a normal recording or reproducing mode (hereinafter referred to as the SP mode). In this instance, with a recording operation performed in the recording or reproducing mode for long time recording or reproduction (hereinafter referred to as the LP mode), all the recording tracks are formed in an overlapped writing manner. Then, it is hardly possible to adequately record and reproduce a video signal.
To solve this problem, it is conceivable to provide the VTR with recording/reproducing heads separately arranged for the SP mode and the LP mode. However, it is a tendency in the recent years to arrange a VTR to have such trick functions as slow motion reproduction and still picture reproduction. These functions require additional heads arranged solely for such purposes. Therefore, the above-stated solution is not desirable as it further increases the number of heads.
Further, it is also a recent tendency to make further reductions in the size of a VTR. To meet this tendency, there have been proposed and practicalized some VTR's of the kind in which an "n" number ("n" being an integer which is at least 3) of video heads are mounted on one and the same cylinder and arranged to have equal phase difference among them; and recording or reproduction is carried out with a recording tape wound around the cylinder at a wrap angle of at least ##EQU1## If the VTR of this kind is provided with heads which are respectively arranged solely for the SP mode and solely for the LP mode, the number of heads becomes at least 2n. Such an increased number of heads brings about various problems including a shorter life of the magnetic tape; difficulty in carrying out adjustment work on the rotary head cylinder; an increase in cost of the VTR; signal deterioration due to crosstalk between rotary transformers; difficulty in reducing the size and thickness of the rotary head cylinder; and so on.